R&D Report 1954-37 : NTSC colour television system: Interference on monochrome television receivers by the chrominance subcarrier. L.C. Munn, R.D.A. Maurice The tests described were undertaken during the period in July for which a simulated chrominance signal was radiated from the Alexandra Palace, and, a far as possible, the radiated signal was used for the purpose of the tests. Measurements were made at Kingswood on a group of six domestic television receivers, the main objects being: a. To measure at the sound output of each receiver the amount of breakthrough or crosstalk caused by the subcarrier modulation, and to compare this with the measured background noise which was audible from the loudspeaker when the receiver was functioning normally, that is, when no chrominance signal was present. b. To assess the perceptibility of the dot structure resulting from subcarrier interference and to compare this with the perceptibility of the normal raster structure. The results indicate that in test a the amount of interference on the sound channels of the receivers was so small as to approximate to the normal breakthrough of vision on sound. In test b the average of the viewers could still perceive the normal raster lines at a distance twice that at which they could see the dot pattern due to the subcarrier. Two subsidiary features have been examined during the preparatory work for the two main tests which form the substance of this report. They are: i. A reason for the subcarrier dot pattern appearing brighter than the mean raster illumination. ii. The perceptibility of line structure at various brightness levels. These secondary observations are included as Appendices 1 and 2 respectively.